The present invention reduces encoding distortion in frequency domain encoding compared to conventional techniques, and obtains LSP parameters that correspond to quantized LSP parameters for the preceding frame and are to be used in time domain encoding from coefficients equivalent to linear prediction coefficients resulting from frequency domain encoding. When p is an integer equal to or greater than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], ..., a[p], and É[1], É[2], ..., É[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], ..., a[p], an LSP linear transformation unit (300) determines the value of each converted frequency domain parameter ˆ¼É[i] (i=1, 2, ..., p) in a converted frequency domain parameter sequence ˆ¼É[1], ˆ¼É[2], ..., ˆ¼É[p] using the frequency domain parameter sequence É[1], É[2], ...,
